1. Field of the Invention
The present invention relates to a projection exposure apparatus which is used when manufacturing a semiconductor element, a liquid crystal display element, or the like by a photolithographic process.
2. Description of the Related Art
In a photolithographic process for making a semiconductor element or liquid crystal substrate or the like, a projection exposure apparatus is employed to expose a pattern image on an original plate such as a reticle or the like onto a photosensitive substrate such as a wafer or the like. With this projection exposure apparatus, for the reason described below, high accuracy positional adjustment has been necessary between an optical system for illumination and an exposure apparatus main body, in other words between an illumination optical system for illuminating an original plate at a uniform illumination distribution, and an exposure apparatus main body for forming a predetermined circuit pattern on a photosensitive substrate by projecting a pattern provided upon the illuminated original plate onto the photosensitive substrate via a projection optical system. That is, the line width of the circuit pattern formed on the photosensitive substrate is increased or decreased in accordance with the amount of exposure of the pattern image which is formed via the above described projection optical system on the photosensitive substrate. Accordingly, in order to limit wide variation of the line width of the circuit pattern, it is necessary to illuminate the pattern which is provided on the original plate at as even an illumination level as possible, and to keep the unevenness of illumination low. Due to this, the positioning accuracy required between the elements which constitute the illumination optical system has become high.
For the above reason, it is only possible for the various elements of the illumination optical system to be separated at portions with a comparatively low value of positioning required accuracy, and as a result it has been necessary to provide the portions which constitute most of the weight of the illumination optical system and the exposure apparatus main body as one unit. Due to this, it has been necessary to provide a frame in the exposure apparatus main body to support the illumination optical system, and because of this the exposure apparatus main body has become large in size. Further, this has led to weight increase of the exposure apparatus main body.
On the other hand, with the exposure apparatus main body, vibration from the surface of the floor is intercepted by an active vibration prevention system, and further vibration generated when heavy parts such as a wafer stage or the like provided inside the exposure apparatus main body accelerate or decelerate during their movement is also suppressed. The active vibration system comprises air springs (hereinafter termed air mounts) which support the exposure apparatus, voice coil motors (hereinafter termed VCMs) which impart thrusts in predetermined directions to the exposure apparatus main body, acceleration sensors which detect vibrations of the exposure apparatus main body, and a feedback control system for controlling the amounts of air supplied to the air mounts and the thrusts of the VCMs and the like based upon vibrations of the exposure apparatus main body detected by the acceleration sensors, etc. According to the above construction, the active vibration prevention system interrupts the transmission of vibrations from the outside, and suppresses vibrations generated within the exposure apparatus main body.
(The Problem of Load on the Air Mounts)
However, along with the fact that the weight of the exposure apparatus main body is increased as described above, the load on the air mounts also becomes large, and the capacity of the compressed air supply which is ordinarily provided in the workshop in which the projection exposure apparatus is set up has sometimes become insufficient. Further, in the same way, the VCMs are also required to be high thrust ones, and the amount of heat generated when driving the VCMs also increases. This heat generation causes air turbulence, and in some cases the measurement accuracy of interferometers for measurement of the position of the wafer stage etc. has become deteriorated.
(Problem of Vibration Transmission to the Exposure Apparatus Main Body)
Further, in the case that the projection exposure apparatus is a scanning exposure method one, a reticle blind which is provided in the illumination optical system is driven during exposure. In a projection exposure apparatus from which an accuracy on the nanometer level is required it has happened that vibration generated at this time cannot be ignored. This will be explained below.
The reticle blind is a device for preventing non-required light emitted by the illumination light in a range of the original plate outside the pattern portion from impinging upon the photosensitive substrate. And the operations of opening it before the beginning of scanning exposure action and closing it after completion are repeatedly performed. It has happened that during these opening and closing operations, vibration generated from a reticle blind opening and closing drive mechanism which has employed a stepping motor and a ball screw or the like, has exerted an influence upon the accuracy of projection exposure, as will be explained below.
When scanning exposure is being performed, the original plate is moved under a band shaped illumination region formed by the optical system for illumination, in the short direction of the band shaped illumination region. A pattern on the original plate which is illuminated in a band shape is formed is as a band shaped pattern image on the photosensitive substrate by the projection optical system. At this time, by making the photosensitive substrate move in the opposite direction from the movement direction of the original plate, and moreover by making the ratio of the movement speeds of the original plate and of the photographic substrate and the projection ratio of the projection optical system agree, a projection image of the pattern is exposed onto the photographic substrate, as it were like a slit camera.
If during scanning exposure the above described ratio of speeds is not kept constant, distortion is generated in the circuit pattern which is formed upon the photosensitive substrate. In detail, when starting to move both the original plate and the photosensitive substrate they are both accelerated, but exposure is performed after reaching a constant speed. In order to perform this acceleration, it is necessary to start mutually moving the original plate and the photosensitive substrate from portions outside the range of exposure, and at this time the above described reticle blind is kept closed so that unnecessary light should not impinge upon the photosensitive substrate. And the reticle blind is opened just before the arrival of the pattern region of the original plate in the band shaped illumination region which is formed by the optical system for illumination is imminent. Moreover a frame shaped light interception band (so called xe2x80x9cchromexe2x80x9d) is formed surrounding the pattern region, and, since the width of this frame shaped light interception band is greater than the dimensions of the short side of the band shaped illumination region, a light interception state is maintained by the above described light interception band after the reticle blind has been completely opened. Scanning scanning exposure starts as the arrival of the head portion of the pattern region of the original plate in the band shaped illumination region becomes imminent. The arrival of the end edge portion of the pattern region of the original plate in the band shaped illumination region becomes imminent just before this scanning exposure is completed, and next the arrival of the frame shaped light interception band (the xe2x80x9cchromexe2x80x9d) becomes imminent, and scanning exposure is finished. After this the reticle blind is closed.
As explained above, the opening and closing operation of the reticle blind is performed directly before and directly after scanning exposure, but it can happen that vibration generated during opening and closing operation of the reticle blind may persist during scanning exposure and may exert an influence upon exposure accuracy. Further, a pump or the like may be provided for gas supply or the like to an excimer laser light source etc., and it may happen that this pump becomes a source of vibration which exerts an influence upon exposure accuracy.
A first objective of the present invention is to propose a projection exposure apparatus in which the exposure optical system can be separated from the portions for which the required accuracy of positioning is high, and in which by doing this the exposure apparatus main body can be made more compact and can be reduced in weight.
A second objective of the present invention is to propose a projection exposure apparatus in which sources of vibration are separated from the exposure apparatus main body, and with which it is possible to obtain high exposure accuracy.
The first projection exposure apparatus according to the present invention that illuminates an original plate on which a predetermined pattern is formed with light emitted from a source of light for exposure, and projects an image of the pattern onto a subject material for exposure, comprises: an optical system for illumination that conducts light emitted from the light source for exposure to the original plate; a projection optical system that is provided between the original plate and the subject material for exposure and projects the pattern on the original plate onto the subject material for exposure; a main body section that is provided as a separate unit from at least one portion of the optical system for illumination and supports the projection optical system; an original plate stage that holds the original plate and is movable; a drive frame that is movable according to a reaction force generated when the original plate stage moves, in a direction reverse to a movement of the original plate stage; and a positioning drive device that performs driving for positioning so as to keep an amount of relative positional deviation between the at least one portion of the optical system for illumination that is provided as a separate unit from the main body section, and the main body section, within a predetermined value.
In this projection exposure apparatus, the positioning drive device may perform positioning by driving at least one of the at least one portion of the optical system for illumination that is provided as a separate unit from the main body section, and the main body section.
Also, the main body section may comprise a stabilizing device that keeps the main body section in a stable state; and the positioning drive device may perform positioning by driving the at least one portion of the optical system for illumination. In this case, the stabilizing device of the main body section may comprise an active vibration prevention device that actively prevents vibration of the main body section.
Also, the optical system for illumination may further comprise a variable illumination visual field aperture device that can adjust a range of illumination of the original plate by the light source for exposure; and in the optical system for illumination a portion disposed on a light incident surface side of the variable illumination visual field aperture device including the variable illumination visual field aperture device may be provided as a separate unit from the main body section. In this case, the positioning drive device may perform positioning by driving at least one of the at least one portion of the optical system for illumination that is provided as a separate unit from the main body section, and the main body section. Or the main body section may use light whose illumination range has been adjusted by the variable illumination visual field aperture device, and perform scanning exposure between the original plate and the subject material for exposure.
The second projection exposure apparatus according to the present invention that illuminates an original plate on which a predetermined pattern is formed with light emitted from a source of light for exposure, and projects an image of the pattern onto a subject material for exposure, comprises: an illumination optical system that comprises a variable illumination visual field aperture device that can adjust a range of illumination of the original plate by the light source for exposure, and that conducts light emitted from the light source for exposure to the original plate; a projection optical system that is provided between the original plate and the subject material for exposure and projects the pattern on the original plate onto the subject material for exposure; a main body section that is provided as a separate unit from a portion of the optical system for illumination, including the variable illumination visual field aperture device, disposed on the light incident surface side of the variable illumination visual field aperture device, and that supports the projection optical system; a stage that is provided as a separate unit from the main body section and that holds and moves the subject material for exposure.
The third projection exposure apparatus according to the present invention that illuminates an original plate on which a predetermined pattern is formed with light emitted from a source of light for exposure, and projects an image of the pattern onto a subject material for exposure, comprises: a variable illumination visual field aperture device that can adjust a range of illumination of the original plate; an illumination optical system that is provided as a separate unit from the light source for exposure, and that conducts light from the light source for exposure to the original plate; a projection optical system that is provided between the original plate and the subject material for exposure and projects the pattern on the original plate onto the subject material for exposure; and a main body section that is provided as a separate unit from at least a portion of the optical system for illumination, and that supports the projection optical system.
This projection exposure apparatus may further comprise: a positioning drive device that performs driving for positioning so as to keep an amount of relative positional deviation between the at least one portion of the optical system for illumination that is provided as a separate unit from the main body section, and the main body section, within a predetermined value.
The fourth projection exposure apparatus according to the present invention that illuminates an original plate on which a predetermined pattern is formed with light emitted from a source of light for exposure, and projects an image of the pattern onto a subject material for exposure, comprises: an illumination optical system that conducts light emitted from the light source for exposure to the original plate; a main body section that is provided as a separate unit from at least a portion of the optical system for illumination, and that comprises at least one of an original plate stage on which the original plate is loaded and a substrate stage on which the subject material for exposure is loaded; and a frame that is provided as a separate unit from the main body section, and to which reaction force, which is generated when the original plate stage or the substrate stage moves, is transmitted.
In this projection exposure apparatus, the original plate stage or the substrate stage may be driven by a non contact type drive device made up from a movable element and a fixed element, and the movable element may be provided to the original plate stage or the substrate stage while the fixed element is provided to the frame.
The fifth projection exposure apparatus according to the present invention that illuminates an original plate on which a predetermined pattern is formed with light emitted from a source of light for exposure, and projects an image of the pattern onto a subject material for exposure, comprises: a main body section that supports a projection optical system which is provided between the original plate and the subject material for exposure and projects the image of the pattern; an illumination optical system at least a part of which is provided as a separate unit from the source of light for exposure and the main body section and illuminates the original plate; a supply device that is provided as a separate unit from the main body section and the illumination optical system and supplies at least one of the original plate and the subject material for exposure to the projection exposure apparatus.
In the first projection exposure apparatus, the main body section may support the original plate stage to be movable.
The first projection exposure apparatus may further comprise an interferometer that is connected to the main body section and detects a position of the original plate stage.
The second projection exposure apparatus may further comprise a positioning drive device that performs driving for positioning so as to keep an amount of relative positional deviation between the at least one portion of the optical system for illumination that is provided as a separate unit from the main body section, and the main body section, within a predetermined value. In this case, the projection exposure apparatus may further comprise a stage that is provided as a separate unit from the main body section and that holds and moves the subject material for exposure.
The fourth projection exposure apparatus may further comprise an interferometer that is connected to the main body section and detects a position of the original plate stage.
The fourth projection exposure apparatus may further comprise an interferometer that is connected to the main body section and detects a position of the substrate stage.
The fifth projection exposure apparatus may further comprise: a first stage that holds and moves the original plate; and a second stage that holds and moves the subject material for exposure. In this case, at least one of the first stage and the second stage may be hold to be movable.
In the fifth projection exposure apparatus, the source of light for exposure may be an excimer laser light source.